In electronic delivery systems, as in physical mail systems, a recipient""s destination is generally identified by a fixed address. A problem with fixed addresses is that they are accessible to anyone with knowledge of the address. Knowledge of a fixed address permits a sender to use that address as a destination without the destination owner""s permission.
When an undesirable sender obtains a fixed address, the recipient has two options for dealing with it: filtering out unwanted items, or moving to a new address. However, filtering unwanted item is rarely perfect. The efficacy of a filter depends on the nature of the screening criteria. If the criteria are too specific, unwanted items may be mistakenly passed through, and if the criteria are too general, desired items may be mistakenly filtered. Changing a fixed address is even more inconvenient, because it inevitably requires the destination owner to inform all desired senders of the new address.
Another problem with fixed addresses is that they are fully transferable to any third party, along with the implied permission to transmit digital content intact to the address. The recipient has no control over this transferability, and therefore any transfers give the transferee the same ability to deliver items without restriction.